There exists in the prior art a stereoscopic imaging apparatus for forming subject images, which have been obtained by passage through areas of different shooting lenses, on respective ones of image sensors and acquiring different viewpoint images.
In an optical system shown in FIG. 14, light rays L1 and L2 assumed to be parallel from a subject are split left and right by mirrors 151 and 161. The light rays L1 on the right side with respect to the subject are reflected at mirrors 151 and 152 and impinge upon an image forming lens 153. The right-side light rays L1 that have impinged upon the image forming lens 153 form an image on the photoreceptor surface of an image sensor 154. An image from the viewpoint of the right eye is obtained in the image sensor 154. Similarly, the light rays L2 on the left side with respect to the subject are reflected at mirrors 161 and 162 and impinge upon an image forming lens 163. The left-side light rays L2 that have impinged upon the image forming lens 163 form an image on the photoreceptor surface of an image sensor 164. An image from the viewpoint of light rays L2 that have impinged upon the image forming lens 163 form an image on the photoreceptor surface of an image sensor 164. An image from the viewpoint of the left eye is obtained in the image sensor 164. Left-and-right parallax images can be obtained. An image sensing apparatus for acquiring left-and-right parallax images in this manner has been disclosed in Japanese Patent Application Laid-Open No. 2010-81580.
Further, there is also a technique for creating and storing a parallax map, which represents depth distribution, from such parallax images. According to Japanese Patent Application Laid-Open No. 2011-19084, a depth information generating unit generates depth maps with regard to respective ones of a left-eye image and right-eye image from the left-eye image and right-eye image, which are for displaying a generated stereoscopic image. An imaging apparatus or imaging method for creating a parallax map from parallax images has been disclosed in Japanese Patent Application Laid-Open Nos. 2008-116309, 2008-141666, 2009-14445 and 2010-226500.
Examples of a stereoscopic imaging apparatuses capable of outputting a plurality of images having a phase difference by pupil division with respect to a beam of light from a single imaging optical system have been described in Japanese Patent Application Laid-Open Nos. 2003-7994, 2001-12916 and 2001-16611. For example, Japanese Patent Application Laid-Open No. 2003-7994 discloses a solid-state image sensor in which a multiplicity of pixels are arrayed on the same imaging plane for opto-electronically converting the image of a subject formed on the imaging plane to thereby generate an image signal. The solid-state image sensor is characterized in that the multiplicity of pixels are partitioned into two groups and the received-light incidence angles of the pixels in each group are made different from one another.
In the stereoscopic imaging apparatuses capable of outputting a plurality of images (of different viewpoints) having a phase difference by pupil division with respect to a beam of light from a single imaging optical system, as described in Japanese Patent Application Laid-Open Nos. 2003-7994, 2001-12916 and 2001-16611, some of the pixels of the image sensor are used in outputting a parallax image in the leftward direction and the remaining pixels are used in outputting an image in the rightward direction. If the pixels (referred to as “phase-difference pixels” below) that output left-right parallax are arrayed on the image sensor, which has a square pixel array, uniformly along the column direction (the horizontal direction), the number of horizontal pixels that can be used for each of the left and right parallax images will be half the proper pixel number which does not have pixels that output parallax. That is, in a case where the left and right images are each observed separately as two-dimensional images, the horizontal resolution will be half in comparison with a two-dimensional image that is output from the proper image sensor that does not possess phase-difference pixels.
Naturally, if two image sensors using an optical system of the kind shown in FIG. 14 are provided, then a resolution conforming to the numbers of pixels of each of the image sensors can be obtained and therefore resolution will not be sacrificed. However, a collimating optical system (not shown), the mirrors 151, 152, 153, 154 and the two image sensors 156 and 164, which originally are not required, become necessary. This is disadvantageous in terms of cost.